Over the past 50 years, there have been substantial improvements in the genetic production potential of ruminant animals (sheep, cattle and deer). Levels of meat, milk or fiber production that equal an animal's genetic potential may be attained within controlled feeding systems, where animals are fully fed with energy dense, conserved forages and grains. However, the majority of temperate farming systems worldwide rely on the in situ grazing of pastures. Nutritional constraints associated with temperate pastures can prevent the full expression of an animal's genetic potential. This is illustrated by a comparison between milk production by North American grain-fed dairy cows and New Zealand pasture-fed cattle. North American dairy cattle produce, on average, twice the milk volume of New Zealand cattle, yet the genetic base is similar within both systems (New Zealand Dairy Board and United States Department of Agriculture figures). Significant potential therefore exists to improve the efficiency of conversion of pasture nutrients to animal products through the correction of nutritional constraints associated with pastures.
The ability to control flowering in C3 monocotyledonous plants, such as forage grasses (e.g. perennial ryegrass and tall fescue) and cereals (e.g. wheat and barley), has wide ranging applications. For example, controlling flowering in forage grasses offers the ability to halt the increase in syringyl lignin that is associated with the decrease in digestibility of forage at this time. In addition, it offers the ability to control the spread of genetically modified organisms, as well as lowering the incidence of allergies associated with ryegrass pollen levels. Other advantages include the ability to induce the time of flowering to suit farming practices better. To achieve this, a flowering control gene would have to be placed under the control of an inducible promoter and the endogenous flowering genes would need to be silenced. A number of genes are known to control flowering in a range of species.
A simple model has been proposed for the genetic network regulating flowering time and flower development in Arabidopsis. In Arabidopsis there are three genetic pathways that control flowering time (Reeves and Coupland, Curr. Opin. Plant Biol. 3:37-42, 2000). The long-day pathway represented by GIGANTEA (GI) and CONSTANS (CO), and the autonomous pathway represented by LUMINIDEPENDENS (LD), FLOWERING TIME CONTROL PROTEIN (FCA) and FLOWERING LOCUS C (FLC) are likely integrated through FLOWERING LOCUS T (FT) and AGAMOUS-LIKE20 (AGL20) to promote activation of meristem identity genes LEAFY (LFY), APETALA1 (AP1) and CAULIFLOWER (CAL). The vernalization pathway represented by FRIGIDA (FRI), feeds into the autonomous pathway upstream of FLC. The giberellin pathway (GA) is represented by gibberellic acid insensitive (GAI) that leads to the activation of LFY. The TERMINAL FLOWER 1 (TFL1) restricts the expression of the meristem identity genes to the floral meristems, thereby promoting the patterned expression of floral organ identity genes such as APETALA2 (AP2), APETALA3 (AP3), PISTILATA (PI), and AGAMOUS (AG). These floral identity genes are also affected by other regulatory genes such as AINTEGUMENTA (ANT), UNUSUAL FLORAL ORGANS (UFO) and SUPERMAN (SUP). Homologs of some of these genes have been identified in other monocots such as maize and rice as well as the dicot species Antirrhinum, where they play a role that is either similar or divergent to that of the Arabidopsis gene in flowering. For example, some key regulatory flowering genes are conserved between rice and Arabidopsis, however, the regulation of FT by CO is reversed in the two species under long day conditions (Hayama et al., Nature 422, 719-722, 2003).
Both genetic and molecular studies have led to the proposal of the ABC model for floral organ identity (Ma and DePamphilis, Cell 101:5-8, 2000). The Arabidopsis B function genes, APETALA3 (AP3) and PISTILATA (PI), are required to specify petal and stamen identities. The Arabidopsis meristem identity gene, LFY, is required for normal levels of AP3 and PI expression (Weigel and Meyerowitz, Science 261:1723-1726, 1993). The Arabidopsis gene UFO plays a role in controlling floral meristem development and B function, and the activation of AP3 by LFY requires UFO (Lee et al., Curr. Biol. 7:95-104, 1997). The ASK1 gene regulates B function gene expression in cooperation with UFO and LFY in Arabidopsis (Zhao et al., Development 128:2735-2746, 2001; Durfee et al., Proc. Natl. Acad. Sci. USA 100:8571-8576, 2003).
It has been suggested that UFO and ASK1 may be subunits of a three-component SCF (SKP1, cullin, F-box) ubiquitin ligase. In addition, ASK1 shows high sequence identity to the yeast SKP1 protein. Ubiquitin ligase is part of the ubiquitin-dependent protein degradation pathway; this suggests that UFO and ASK1 may regulate the level of other regulatory proteins that control cell division and transcription during floral development.
FCA encodes a strong promoter of the transition to flowering in Arabidopsis. Arabidopsis fca mutants flower late in both long days and short days. FCA has been cloned and shown to encode a protein containing two RNA-binding domains and a WW protein interaction domain (Macknight et al., Cell 89:737-745, 1997). The regulation of FCA expression is complex. FCA pre-mRNA is alternatively processed resulting in four types of transcripts of which FCA-γ is the active form. Recent studies have shown that FCA functions with FY, a WD-repeat protein, to regulate 3′ end formation of mRNA and control the floral transition (Simpson et al., Cell 113:777-787, 2003). Plants carrying the FCA gene fused to the strong constitutive 35S promoter flowered earlier, and the ratio and abundance of the different FCA transcripts were altered. The rice genome contains a single copy homolog of FCA (Goff et al., Science 296:92-100, 2002).
The FT/TFL gene family encodes proteins with homology to phosphatidy-ethanolamine binding proteins that have been shown to be involved in major aspects of whole-plant architecture. FT acts in parallel with the meristem-identity gene LFY to induce flowering of Arabidopsis (Kardailsky et al., Science 286:1962-1965, 1999). It is similar in sequence to TFL1, an inhibitor of flowering (Ohshima et al., Mol. Gen. Genet. 254:186-194, 1997). The crystal structure of the Antirrhinum FT/TFL homolog, CENTRORADIALIS (CEN) suggests that it has a role as a kinase regulator (Banfield and Brady, J. Mol. Biol. 14:1159-1170, 2000). The rice genome contains 17 members of the FT/TFL gene family; one member is most similar to TFL, and nine are more similar to FT. A functional FT ortholog from rice, Hd3a, was detected as a heading date QTL and has the same regulatory relationship with rice CONSTANS homolog, Hd1, that Arabidopsis FT has with CO (Kojima et al., Plant Cell Physiol. 43:1096-1105, 2002). A TFL1-like gene from Lolium perenne has been isolated and characterized (Jensen et al., Plant Physiol. 125:1517-1528, 2001). Arabidopsis plants over-expressing the LpTFL1 gene were significantly delayed in flowering and the LpTFL1 gene was able to complement the severe tfl1-14 mutant of Arabidopsis. 
The Arabidopsis gai (gibberellic acid insensitive) mutant allele confers a reduction in gibberellin (GA) responsiveness, thereby playing a role in the GA regulated control of flowering. GAI contains nuclear localization signals, a region of homology to a putative transcription factor, and motifs characteristic of transcriptional co-activators (Peng et al., Genes Dev. 11:3194-3205, 1997). Homologs from other plant species have been identified, for example, RHT from wheat, D8 from maize and SLR1 from rice (Ikeda et al., Plant Cell 13:999-1010, 2001). Four rice sequence homologs of the Arabidopsis GAI gene have been identified in the rice genome (Goff et al., Science 296:92-100, 2002).
Alongside CONSTANS (CO), GIGANTEA (GI) exerts major control over the promotion of flowering under long days in Arabidopsis. Mutations in the Arabidopsis thaliana GI gene cause photoperiod-insensitive flowering and alteration of circadian rhythms. GI, originally described as a putative membrane protein (Fowler et al., EMBO J. 18:4679-4688, 1999), was recently determined to be a nuclear protein involved in phytochrome signaling (Huq et al., Proc. Natl. Acad. Sci. USA 97:9789-9794, 2000). GI is believed to function upstream of CO, because the late-flowering phenotype of GI mutants is corrected by CO over expression (Fowler et al., EMBO J. 18:4679-4688, 1999). A single putative GI ortholog exists in rice, based on the similarity of the predicted GI amino acid sequence. Overexpression of OsGI, an ortholog of the Arabidopsis GIGANTEA (GI) gene in transgenic rice, caused late flowering under both SD and LD conditions (Hayama et al., Nature 422, 719-722, 2003).
The indeterminate1 (id1) mutation in maize results in plants that are unable to undergo a normal transition to flower development and remain in a prolonged state of vegetative growth. The ID1 gene plays an important role in controlling the transition to flowering and maintaining the florally determined state. The ID1 gene was cloned by transposon mapping in maize (Colasanti et al., Cell 93:593-603, 1998). The ID1 gene encodes a protein with zinc finger motifs, indicating that it functions by transcriptional regulation of flowering. Expression studies showed that ID1 is expressed in immature leaves and not the shoot apex, and may therefore mediate the transition to flowering by regulating the transmission or synthesis of a signal for flowering. ID1 functional homologs have not been in identified in Arabidopsis but putative ID1 gene sequences have been identified from rice (Goff et al., Science 296:92-100, 2002).
LEUNIG (LUG) is a key regulator of the Arabidopsis floral homeotic gene AGAMOUS. Mutations in LEUNIG cause ectopic AGAMOUS mRNA expression in the outer two whorls of a flower, leading to homeotic transformations of floral organ identity as well as loss of floral organs. LEUNIG is a glutamine-rich protein with seven WD repeats and is similar in motif structure to a class of functionally related transcriptional co-repressors. The nuclear localization of LEUNIG is consistent with a role of LEUNIG as a transcriptional regulator (Conner and Liu, Proc. Natl. Acad. Sci. USA 97:12902-12907, 2000). Another regulatory gene, SEUSS, has recently been identified that functions together with LEUNIG to regulate AGAMOUS (Franks et al., Development 129:253-263, 2002).